"The only thing that ever really frightened me during the war was the U-boat peril," admitted Winston Churchill after World War II. This 2002 documentary from the BBC examines the German U-boats, and investigates how close they came to being the deciding factor in the global conflict. The three-part program tells the story of the Battle of the Atlantic, which lasted for the duration of the war and involved massive loss of lives and ships. "The Grey Wolves" chronicles the story of Hitler's submarines and their threat to starve Britain into submission. Under the leadership of Admiral Karl Doenitz and his "wolf packs" they nearly succeeded, with huge numbers of merchant ships being sunk from 1939 to 1942. "Keeping Secrets" describes the capture of an Enigma machine and the invention of radar. "The Hunted" profiles the tactics of Allied forces on land and sea that led to victory. Archival footage shows Churchill meeting British and U.S. Navy sailors and Hitler with some of the top U-boat commanders, and numerous eyewitness accounts by U-boat commanders, Royal Navy hunters, merchant seamen, airmen, and code-breakers.